Parting compound containing chromium oxide manganese dioxide and a liquid inorganic carrier

ABSTRACT

A parting composition, including a mixture of manganese dioxide and an oxide of chromium, can be applied to the contacting surfaces of metal sheets and plates in assemblies to be hot worked. The parting composition prevents adhesion between those surfaces to which it is applied. After hot working, the composition can be easily removed from the treated surfaces with an acid pickling solution.

United States Patent McGlynn [4 1 Apr. 25, 1972 s41 PARTING COMPOUND CONTAINING 2,588,260 3/1952 Lynch et a1 .252/471 CHROMIUM OXIDE MANGANESE 1,995,349 3/1935 Heinicke ....1 17/129 2.061,470 11/1936 Larson ....252/471 gL% g A LIQUID INORGANIC 1,955,547 4/1934 lngersoll ...29/470.9 2,109,010 2/1938 lngersoll ...29/470.9 [72] Inventor: James J. McGlynn, Paoli, Pa. 2,711,966 6/1955 Watson..... ...29/470.9 3,059,324 10/1962 Goff ...29/470.9 [73] A gn L n Steel mp ny, C i 3,237,298 3/1966 Ma ..29/458 [22] Filed: 1969 Primary Examiner-Theodore Morris [21] App]. N0.: 795,044 Atlorney-Mason, Mason &'Albright [57] ABSTRACT [52] U.S. CL... ..106/286, 29/4709 51 Int. Cl. ..C08h17/24 A Parting composition, including a mixture of manganese 58 Field of Search 106/286, 84,66; 117/129; dioxide and an Oxide ofshmmivm, can be applied to 29/47o 9 tacting surfaces of metal sheets and plates in assemblies to be hot worked. The parting composition prevents adhesion [56] References Cited between those surfaces to which it is applied. After hot working, the composition can be easily removed from the treated UNITED STATES PATENTS surfaces with an acid pickling solution.

2,959,577 1 H1960 Hogan ..260/94.9 D 3 Claims, No Drawings PARTING COMPOUND CONTAININGCI-IROMIUM. OXIDE MANGANESE DIOXIDE AND A LIQUID INORGANIC CARRIER This invention is directed to a parting composition useful in preventing adhesion between adjoining metal surfaces in the hot working of clad assemblies. Clad assemblies are usually prepared as composite assemblies in which a relatively thin sheet of corrosion-resistant alloy is adhered-to a thicker and comparatively less expensive backing plate. Thus such alloys as chrome, chrome-nickel steel, chrome-nickel-molybdenum steel, nickel, nickel alloys, copper, and copper alloys are welded to plates of plain carbon or low alloy steel.

The usual method of welding sheets to plates is to form an assembly by superimposing a corrosion-resistant layer over a backing plate, excluding air from the area to be welded and thereafter hot working the assembly.

In the interest of economy, a plurality or pack of assemblies is frequently formed before hot working and the pack is heated and rolled as a unit to effect welding within each assembly. In general, parting compositions, both organic based and water based are used to prevent welding between the adjacent surfaces of individual assemblies within the pack.

Most parting compositions contain refractory oxides as'the principal weld-preventing ingredient and refractory chrome oxides such as Cr or CrO are commonly used. Manganese dioxide has also been used as a refractory in parting compositions but not in combination with chromium oxides in the same coating. The usual and most convenient mode of applying parting compositions is to form a slurry of the powdered refractory oxide and paint the surfaces to be treatedwith the slurry when assembling the pack. Thereafter the pack can be subjected to hot working without the danger of welding the individual assemblies to one another. Hot working, in the instance of welding stainless steel to mild steel, is normally carried out at about 2,200 2,400 E, usually by rolling the pack until a reduction of at least 2 to l in thickness is reached.

After hot working, the individual assemblies are'separated from one another. It is then necessary to remove the parting composition which becomes tightly adherent when chrome oxides are used and this is effected by blasting or exposing-the assemblies to a molten caustic bath followed by acid pickling.

The present invention involves the incorporation of manganese dioxide in parting compounds containing chromeoxides with the advantage that after hot working, the residual parting compound can be easily removed by an acid'mixture. Thus, with the parting composition of the presentinvention, it is not necessary to blast or use a molten caustic treatment followed by acid pickling.

It is therefore an object of thepresent invention to provide a new parting composition and process forusing same whichare effective to prevent welding during hot working and which result in surfaces that can be easily cleaned following exposure to heat and pressure. These and other objects will be'apparent from the disclosure set forth below.

A mixture of manganese dioxide and -an oxide of chromium, both in particulate form, preferably finely milled to 1-10 micron size when incorporated in an organicoraqueouss'lurry, operates to prevent welding under'hot working-conditions. Mixtures of finely divided manganese dioxide and chromium oxide can be used without a binder, but for ease of application, a slurry of the mixture with a binder is used. An-organic binder such as that disclosed in U. S. Pat. No. 3,237,298 is suitable in the ratios and amounts disclosed. Preferably,'how.- ever, a water-based slurry is used, such as the conventional 2 percent by weight sodium silicate solution.'0ther additives, such as sand, crushed firebrick, clay and the like can be added if desired.

The amounts of chromium oxide and manganese dioxide to be used can best be expressed in volume ratios of Cr O to MnO Broadly, about 0.01 5 parts 0 0,10 1 part MnO is operative. Preferably, about 0.3 1 parts Cr O to 1 part M10, is used.

Chromium oxide is a superior refractory whereas manganese dioxide imparts superior cleaning characteristics to the parting composition. Higher ratios of Cr,0, than 1 part of Cr O to 1 part of- MnO by volume do not clean as readily as the preferred'ratio. Lower ratios of-Cr,0, than 0.2 parts Cr,0, to 1 part of MnO leave rougher surfaces after being cleaned by acid pickle.

As stated above, the mixture of manganese dioxide and oxide of chromium can be used either in an organic slurry such as a conventional ethyl acetate base with nitrocellulose hinder, or in anaqueous slurry with a water glass base binder. A water-basedslurry is more easilysprayed and therefore is preferred. In either case, however, a dried coating thickness of about-0.001 to0.003 inches is operative.

EXAMPLE 1 Two Type 304 ELC stainless steel insert plates each measuring 102% X 82 X 9/16 inch were spray painted with 1,600 cc (800 cc on each insert) of a mixture containing 3 lbs. of MnO and 1 lb. of'Cr O in 4 percent water glass(4.percent water glass solution made by diluting N type sodium silicate solution withwater 25 volumes of water 1 volume N).

Material coverages amounted to 0.0256 lb. mom. and 0.0085lb. Cr o lft. of insert.

The insertsinan assembly with steel backing-plates were hot rolled to a 5.4/1 ratio and cleaned in HNO I-IF acid. The l-INO HF acidused was approximately 10 parts by volume of commercial nitric acid plus 2 volume parts of hydrofluoric acid'plus 88 volume parts of water in a tank holding approximately 12,000 gallons. The acid-temperature was F. and the dip time was 10 minutes. Removal of the parting compound under these conditions'was substantially complete.

EXAMPLE 2 Two Type 316 ELC stainless steel insert plates measuring 98% X 82 X l 1/ 16 inch were spray painted with 2,000 cc (1,000 cc on each insert) containing 3.6 lbs. MnO, and 1.2 lbs. C50 The liquid carrier-binder was a 40 percent water dilution of Type 48 lithium polysilicate solution (Du 'Pont).

The material coverages amount to 0.032 lb. MnO per square foot-and 0.01 1 lb. Cr,O per-square foot of insert.

These inserts, after being placed in an assembly with backing steels, were hot rolled toa 8%[1 ratio and cleaned in the same I-INO HF acid mixture as in Example 1. The acid temperature was -l05 F. and a dip time of 10 minutes was used. Again the parting compound was effectively removed. The amount and type of binder used is not critical so long as the oxide particles are maintained discrete. In the'above examples, a 4 percent water glassaqueous solution and a water based .polysilicate solution were used but it will be appreciated that the specific composition and type of water glass and amount can vary widely. Similarly, other binders will suggest themselves and can be substituted for those specifically disclosed.

Following hot working, the individual assemblies are separated and their-surfaces-cleaned with'an acid pickle. One acid ,pickle 'found to be effective forremoving residual parting compound is a mixture of nitr ic acid'and hydrofluoric acid. A

dilute acid mixture of l-INO and HF is capable of. dissolving and removing the residual parting composition of the present invention. The acid mixture referred to in the examples is the same commonly used in the trade to pickle, brighten and passiva'te stainless steels.

The dissolved iron content in the acid mixture of HF and I-INO should not :exceed about 4 percent by weight for best results in removing the parting composition residuals. Higher than '4 percent by weight dissolved iron slows down the removal of the parting compound to some extent. In the above Examples l and 2,the-dissolved iron content was 3.05 percent and 3.73 :percent respectively.

What is claimed is:

l. A panting composition for use as a coating of adjoining metal surfaces topreve'ntadhesion during hot working operations which is characterized by superior cleaning properties 2. The composition of claim 1 wherein the slurry 'is water based with water glass as a binder.

3. The composition of claim 1 wherein the oxide of chromium is Cr O and the volume ratio of C50, to MnO, is about 0.3 l to l. 

2. The composition of claim 1 wherein the slurry is water based with water glass as a binder.
 3. The composition of claim 1 wherein the oxide of chromium is Cr2O3 and the volume ratio of Cr2O3 to MnO2 is about 0.3 - 1 to 